The present invention broadly relates to semiconductor processing equipment, and deals more particularly with an interlock system for controlling the flow of gas or other fluid mediums into a processing chamber.
Manufacturing processes for producing semiconductor devices employ a variety of techniques and processes that require the use of reactive gasses combined in precise amounts or ratios. For example, one such process is chemical vapor deposition (CVD) which involves the growth of thin films wherein very high quality films are deposited onto a heated substrate. CVD processes are widely used for forming various layers during integrated circuit fabrication. CVD processes generally involve a decomposition of a precursor gas mixture, at the surface of the heated substrate, to form components which are the chemical precursors of the desired film composition. The CVD process is carried out in a sealed chamber which is evacuated before the selective introduction of reactive gasses. These reactive gases are typically introduced in a serial manner to effect successive process steps. Typically, the reactive gases are delivered to the chamber from individual sources through a series of conduits and valves. In many cases, a combination of gases and/or liquids are introduced into the chamber during a particular process step. In other cases, only a single gas or liquid is introduced into the chamber during a particular process step. In any event, it is often critical that the precise amounts of the gas or liquid be introduced into the chamber so that carefully matched ratios of gases/liquids are maintained, otherwise the desired process results are not achieved, and in some cases, the introduction of different gases outside established ratios may result in a highly volatile, and possibly explosive mixture. Among the liquid chemicals that are critical to introduce in precise amounts are TEPO, TEB and TEOS. Similarly, improper match ratios of boron, phosphine, TEOS, may form BEPSG film side-etch of wafers, thereby resulting in scrap.
A variety of flow control devices have been created to assist in carefully controlling the flow of gases and liquids into the processing chamber, but even these devices are subject to error. For example, mass flow controllers (MFCs) are frequently connected between an incoming source of gas or liquid and the chamber in order to precisely control flow, thus permitting careful ratio matching of the various liquid or gas chemicals used to carry out a particular processing step. One of the problems creating errors where MFC""s are used results from the fact that there is some degree of electrical xe2x80x9covershootxe2x80x9d of the valve control signal when the mass flow control valve is initially opened to introduce a new chemical into the chamber. This overshoot is an electrical phenomena in which the control signal commanding the valve to open overshoots its normal value. However, since the MFC is a proportional control device, the electrical overshoot manifests itself in a proportionate flow overshoot passing through the valve, thus allowing a greater than desired amount of the gas or liquid to be introduced into the chamber. Existing protective devices are limited to sensing catastrophic failures or malfunctions of MFC""s and similar valves. For example, existing protective devices monitor the actual flow rate into the chamber and compare it to a set flow rate over a fairly long length of time during the process step. If the flow rate exceeds the set point for this prolonged period it is assumed that the valve has malfunctioned and the processing operation is shut down. Such protective devices do not, however sense transient overshoot phenomena which prevent precise matching of the ratios of chemicals introduced into the chamber. In other words, the prior art protective devices are not capable of detecting real time flow spikes during a processing operation. The present invention is directed toward solving this problem.
According to one aspect of the invention, a system is provided for controlling the flow of a fluid medium such as a gas or liquid, into a process chamber used to manufacture semiconductor devices. The system includes a mass flow control valve, means for producing first and second signals respectively representing a commanded flow rate and the actual flow rate through the valve. The system further includes a shut off valve for interrupting the flow of fluid into the chamber, and an interlock controller for controlling this shutoff valve. The interlock controller measures the difference between the first and second signals and when this difference is greater that a first pre-selected value, a measurement cycle is commenced in which the peak value of the signal representing the actual flow is recorded. When the peak value the exceeds a pre-selected value, the controller issues a signal that closes the shutoff valve, thereby interrupting the flow of the fluid into the chamber.
According to another aspect of the invention, a method is provided for controlling the introduction of a flowable medium into a processing chamber used to manufacture semiconductor wafers. The method broadly includes the steps of controlling the rate of flow of the medium into the chamber using a flow control valve; measuring the magnitude of the first electrical signal used to control the valve and representing a commanded rate of flow; measuring the magnitude of the second electrical signal representing the actual rate of flow through the valve; determining the difference in value between the first and second signals; commencing a measurement cycle where the difference exceeds a predetermined value; measuring the peak value of the second signal during the measurement cycle; and, interrupting the flow of the medium into the chamber when the measured peak value exceeds a predetermined value. In a preferred form, the signal comparison is delayed a predetermined length of time after the flow control valve is initially opened.
Accordingly, it is the primary object of the intention to provide an interlock control system for semiconductor manufacturing processes which precisely controls the flow of a fluid medium into a processing chamber.
Another object of the intention is to provide an interlocking control system as described above which allows precise matching of the ratios of the multiple chemicals introduced into the processing chamber.
A still further object of the invention is to provide an interlock control system of the type mentioned above which allows real time monitoring of flow spikes so that immediate intervention can be effected to correct or stop a process step.
A still further object of the invention is to provide an interlock control system of the type mentioned which eliminates the possibility of potentially explosive mixtures of gases from forming in the processing chamber.
Another object of the invention is to provide an interlock control system as described above which allows real time monitoring and control of the flow rates in a manner which results in improved processing performance and reduced material scrap.
These, and further objects and advantages of the invention will be made clear or will become apparent during the following description of a preferred embodiment of the invention.